Deirdre McLoughlin on sun 10 oct 99
I used a glaze red lead 42% plus copper iron manganese nickle chrome
each at 2% fired to 1040 degrees.
It volatilized heavily = a green hue on all work that has come out of
the kiln since, when the naked skin gets damp the green grows stronger.
I have refired the kiln 4 times once to 1200 degrees, and soaking there
for half an hour. Another time with a large work to 1180 in the hope
that it would soak up all the floating copper etc.
Is there a quick way to rid my kiln of this problem?
Deirdre McLoughlin, Amsterdam, The Netherlands.
John Hesselberth on mon 11 oct 99
Deirdre McLoughlin wrote:
>----------------------------Original message----------------------------
>I used a glaze red lead 42% plus copper iron manganese nickle chrome
>each at 2% fired to 1040 degrees.
>
>It volatilized heavily = a green hue on all work that has come out of
>the kiln since, when the naked skin gets damp the green grows stronger.
>I have refired the kiln 4 times once to 1200 degrees, and soaking there
>for half an hour. Another time with a large work to 1180 in the hope
>that it would soak up all the floating copper etc.
>
>Is there a quick way to rid my kiln of this problem?
>
>Deirdre McLoughlin, Amsterdam, The Netherlands.
Hi Deirdre,
I can't answer your question with certainty, but this is a good example
of why, if you feel you must use lead in the first place, you should
NEVER use copper in a lead glaze. There are many warnings in the
literature about this. Apparently copper opens the structure of the
glaze and allows both copper and lead to leave the glaze easily. I
suspect the only way you will clean up your kiln now is with multiple
firings (empty-- no use contaminating other pots with lead) to Cone 10 or
to whatever the maximum is for your kiln. Use very, very good
ventilation and preferably leave the kiln room yourself during the
firings. Then, after each firing, test the interior surface of the kiln
with one of those lead testing kits you can get in a hardware store (they
are sold for testing for the presence of lead paint but will also work
for lead on the surface of ceramic materials. Repeat until you don't get
any sign of lead on the test strip.
Then, please, reconsider whether or not you really must be using
lead-based glazes.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
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